Pests (invertebrates, insects, arachnids, mites, larvae thereof, etc.) are annoying to humans for a myriad of reasons. They have annually cost humans billions of dollars in crop losses and in the expense of keeping them under control. For example, the losses caused by pests in agricultural environments include decreased crop yield, reduced crop quality, and increased harvesting costs.
Over the years, synthetic chemical pesticides have provided an effective means of pest control. For example, one prior approach involves the use of complex, organic insecticides, such as those disclosed in U.S. Pat. Nos. 4,376,784 and 4,308,279. Other prior approaches employ absorbent organic polymers for widespread dehydration of the insects. See, U.S. Pat. Nos. 4,985,251; 4,983,390; 4,818,534; and 4,983,389. Use of inorganic salts as components of pesticides has also been tried, as disclosed in U.S. Pat. Nos. 2,423,284 and 4,948,013, European Patent Application No. 462 347, Chemical Abstracts 119(5):43357q (1993) and Farm Chemicals Handbook, page c102 (1987).
However, it has become increasingly apparent that the widespread use of synthetic chemical pesticides has caused detrimental environmental effects that are harmful to humans and other animals. For instance, the public has become concerned about the amount of residual chemicals that persist in food, ground water and the environment, and that are toxic, carcinogenic or otherwise incompatible to humans, domestic animals and/or fish. Moreover, some target pests have even shown an ability to develop resistance to many commonly used synthetic chemical pesticides. In recent times, regulatory guidelines have encouraged the development of potentially less harmful pesticidal compositions via stringent restrictions on the use of certain synthetic pesticides. As a result, elimination of effective pesticides from the market has limited economical and effective options for controlling pests. As an alternative, botanical pesticides are of great interest because they are natural pesticides, i.e., toxicants derived from plants that are safe to humans and the environment. Historically, botanical pesticides, such as tobacco, pyrethrum, derris, hellebore, quassia, camphor and turpentine, have long been used. Of the botanical pesticides, pyrethrum (also known as Caucasian pyrethrum, dalmatic pyrethrum, pesticide chrysanthemum, natural pyrethrum and pyrethrin) has found widespread use.
Pyrethrum, which is extracted from the flowers of a chrysanthemum grown in Kenya and Ecuador, acts on insects with phenomenal speed causing immediate paralysis, while at effective pesticidal concentrations exhibits negligible toxic effects on humans and warm-blooded animals. Use of pyrethrins for industrial or agricultural applications, however, is attendant with several disadvantages. For example, they require frequent treatments because they readily decompose when exposed to direct sunlight. Pyrethrins are also neurotoxic to cold-blooded animals, such as fishes, reptiles, etc. Moreover, the supply of pyrethrins is limited and substantial processing is required to bring the natural product to market, and large-scale production is very expensive. Unless pyrethrins are formulated with a synergist, most initially paralyzed insects recover to once again become pests.
Synergists are compounds that, although typically possessing no direct toxic effect at the dosage employed, are able to substantially enhance the observed toxicity of a pesticide with which they are combined. Synergists are found in most household, livestock and pet aerosols to enhance the action of the fast knockdown pesticides, e.g., pyrethrum, allethrin, and resmethrin, against flying insects. Synergists are required in pesticidal formulations containing pyrethrum, for example, because target insects produce an enzyme (cytochrome P-450) that attacks pyrethrum and breaks it down, thereby making it effective in knocking an insect down, but ineffective for killing in many cases. As such, these synergists act by inhibiting P-450-dependent polysubstrate monooxygenase enzymes (PSMOs) produced by microsomes, which are subcellular units found in the liver of mammals and in some insect tissues that degrade pyrethrum and other pesticidal compounds, such as pyrethrum, allethrin, resmethrin, and the like.
Piperonyl butoxide (PBO) is the main pesticide synergist in commerce. PBO, however, is a synthetic product that has recently been scrutinized by regulatory agencies and certain other groups. As a result, the industry has turned to synthetic pyrethroids, which are very photostable in sunlight and are generally effective against most agricultural insect pests. Pyrethroids are not as safe as pyrethrins, however, and disadvantageously persist in the environment for longer periods. Further, many insects disadvantageously develop resistance to pyrethroids.
Many natural products used as insecticides, including plant essential oils, do not provide adequate control of pests in that they are not very stable and break down quickly, thereby failing to provide toxic residual properties. Products such as pyrethrum, although highly toxic to pests on contact when used properly in pesticidal formulations, are not effective pesticides for many applications because they lack residual properties, thereby increasing the frequency and cost of pesticide applications, as well as increased risk and exposure to the environment.
Accordingly, there is a great need for novel synergistic and residual pesticidal compositions containing no level or substantially lower levels of synthetic pyrethroids, chlorinated hydrocarbons, organophosphates, carbamates and the like. In addition, there is a need for methods for using same that address the problems described above, i.e. are safe to humans and the environment and relatively inexpensive to use in obtaining acceptable levels of insect or pest control.